On the critical state of gap-graded sandy soil

A newly designed and developed triaxial permeameter is presented, along with results from a series of commissioning tests for drained and undrained compression on uniformly graded Fraser River sand. Results are compared to previous studies on Fraser River sand, with generally excellent agreement. The commissioning test series verify that the newly developed device is generating accurate and repeatable results. An experimental study was undertaken, using the triaxial device, to improve the understanding of the mechanics of gap-graded sandy soil. A new sand, Bennett South Moraine (BSM) sand, sampled from the borrow source of the WAC Bennett Dam, is introduced. The effects of reconstitution method, density, and gradation on shear response are examined within a critical state framework for gap-graded BSM sand in drained triaxial compression tests. The critical state of gap-gradations of BSM sand is found independent of reconstitution method and initial void ratio. The strength and void ratio at the critical state are dependent on the finer fraction content, as well as the size ratio of fine to coarse component in a gap-gradation. The findings are attributed to differences in packing characteristics and the relative contribution of each component fraction during shear. The Muir Wood grading state index is examined as a candidate parameter to quantify a change in the critical state with change in gradation, with promising results.Applied Science, Faculty ofCivil Engineering, Department ofGraduat